In view of the recent controversy over the adverse effects of aerosol propellants containing fluorocarbons on the earth's ozone layer and the rising costs of such propellants, a need has arisen for replacements for fluorocarbon propellants. Various hydrocarbons have been suggested as substitute propellants, but in general these propellants are flammable and create a fire hazard.
Carbon dioxide has also been suggested as a propellant for various systems. In fact, carbon dioxide offers many advantages over hydrocarbon and fluorocarbon propellants. It is nontoxic, odorless, does not adversely affect the earth's atmosphere and is non-flammable. The pressure in a container using carbon dioxide gas is less affected by temperatures than fluorocarbons, hydrocarbons and other liquified gas propellants and is thus usable over a greater temperature range than other such propellants. Moreover, compressed carbon dioxide does not have the cooling effect caused by evaporation when liquified gases are used as propellants.
In addition to avoiding the problems encountered in the use of other propellants, the use of a carbon dioxide propellant has commercial advantages. For example, carbon dioxide is many times less expensive than fluorocarbon and hydrocarbon propellants and its cost would be negligible in most products. Thus, its use as a propellant would permit aerosol packaging of many low-priced products which previously have been unavailable in aerosol form due to the propellant costs. Further, smaller weight amounts of carbon dioxide are required for adequate pressure thus resulting in added cost reductions for the manufacturer and providing the user with a higher proportion of product per unit weight of a container's contents. In addition, in view of the relatively high solubility of carbon dioxide in many solvents, less of the container volume must be carbon dioxide for full expulsion of a container's contents.
Despite the above advantages, however, carbon dioxide has not proven satisfactory as a propellant in water-containing aerosol systems due at least in part to the formation of carbonic acid and resultant reduction in the pH of the system. The acidity of water-carbon dioxide aerosol systems have a corrosive effect on many aerosol containers, and may additionally have a deleterious effect on the active ingredients dissolved or dispersed in the aqueous system or impair their storage stability. In addition, the effective amount of carbon dioxide available as a propellant is reduced by the formation of carbonic acid. Also in aerosol systems containing alkaline ingredients, the carbonic acid formed by the water and carbon dioxide reacts to alter or reduce the effective amount of product available for use by the consumer and/or increases the manufacturers' production costs.
Although there have been suggestions for overcoming the problems of using carbon dioxide as a propellant in waterbased aerosol systems, including addition of surfactants, no entirely successful remedy has been forthcoming. Thus, despite its advantages, the use of carbon dioxide as a propellant in water-based aerosol systems have not been possible.
It is, therefore, an object of the present invention to provide a satisfactory water-containing aerosol system employing carbon dioxide as a propellant.
It is another object of the present invention to provide a water-containing aerosol system employing carbon dioxide as a propellant which system does not have a corrosive effect on conventional aerosol containers and thus is storage-stable.
It is a further object of this invention to provide a water-based aerosol system in which carbon dioxide propellant is present in sufficient quantity to expel the entire contents of an aerosol container.
It is yet another object of the invention to provide a water-based aerosol system having a carbon dioxide propellant which does not affect the active components of the product.
It is an additional object of the instant invention to provide a propellant composition for water-containing aerosol systems which avoids the problems and hazards of systems employing hydrocarbon and fluorocarbon propellants.